Manufacturers of certain types of electronics systems, such as infrared (IR) detection and imaging systems, have a need for a hermetically sealed chamber, in which an electronics-containing micro-circuit, such as an infrared-sensing micro-chip that may be internally or externally cooled (depending upon the configuration and application), is placed. In many legacy IR-sensing devices, a cooling fluid, such as liquid nitrogen, supplied from an external cryogenic source, flows through a cooling surface that is situated within a hermetically sealed enclosure. More recently, thermo-electric coolers have been used to cool infrared sensing elements, with both the thermo-electric cooler and the IR-sensing chip cooled thereby being enclosed in a hermetically sealed housing.
Because the multipin plugs that are used to provide external connections for such electronics systems cannot seal to a bundle of wires that connect to the electronics-containing micro-circuits within the hermetically sealed chamber, manufacturers face the problem of having to provide hermetically sealed electrical access to the interior of the housing by means of extremely small multi-pin and socket feed-through connectors. This problem becomes particularly cumbersome and complex with the ongoing demand for reduction in component size.
One type of multi feed-through pin electrical connector, commonly referred to in the industry as a ‘micro-D’ type multipin connector, which contains a relatively large number (e.g., twenty-five) of closely spaced pins, is diagrammatically illustrated in the cross-sectional side view of FIG. 1. As shown therein, at a front or exterior side of the connector, a respective electrical feed-through pin 10 has an exterior distal end 11 that faces the ambient exterior, from which the interior end 16 of a reduced diameter portion 17 of the pin projecting from the interior side of the connector is hermetically sealed. Extending into the pin 10 from the exterior distal end 11 thereof is a longitudinal socket or bore 15, that is sized to receive and engage a respective pin of an associated external multi-pin (e.g., twenty-five pin) plug 30, two pins of which are shown at 31.
A respective feed-through pin 10 is supported and hermetically sealed within a connector body 13 by a generally cylindrically configured, relatively thin-walled, annular sleeve 12 of dielectric material (such as glass), that is inserted over the reduced diameter portion 17 of the pin from its interior end 16, so as to allow the dielectric sleeve 12 to enter into an annular gap 18 between the reduced diameter portion 17 of the pin 10 and a pin-installation bore 14 through the connector body 13. (The dielectric sleeve 12 cannot be placed around the reduced diameter portion 17 of the pin from its socket side, due to the presence of the socket portion of the pin at distal end 11 thereof.)
By the application of heat, the glass material of the sleeve 12 melts and becomes hermetically sealed with both the outer sidewall of the reduced diameter portion 17 of the pin and the interior sidewall of the pin-installation bore, so that the feed-through pin is thereby captured by, and hermetically sealed and supported within the pin-installation bore. Geometry parameters of such a ‘micro-D’ type connector include a center-to-center spacing S between adjacent feed-through pins 10 on the order of fifty mils, a bore diameter BD of the pin-installation bore 14 on the order of forty mils, and a reduced diameter RD of the reduced diameter portion 17 of the interior end of the pin on the order of eighteen mils. Because of this very small feed-through pin-sealing geometry, attaching (e.g., bonding) a (small diameter) wire to the interior end 16 of the reduced diameter portion 17 of the pin is a very difficult and labor intensive task.
Typically, bonding a small diameter wire to the interior end 16 of the reduced diameter portion 17 of the pin is accomplished by extending the wire through a stiff capillary tube and impressing the wire against the interior end of the reduced diameter portion of the pin. Then, through the use of ultrasonic energy and the application of heat and pressure, the end of the wire is bonded to the interior end of the pin—forming what is commonly termed as a ‘ball bond’ at that location. Forming such a ball bond requires the pin to be very stable; if the pin is not stable, it is subject to being deflected or displaced by the application of the ultrasonic energy and pressure, and may result in a poor wire bond, or no bond at all.
This problem of wire-bonding to the interior ends of the reduced diameter portions of such very small sized, feed-through pins has recently become extremely exacerbated by the desire of some equipment manufacturers, such as IR sensor equipment manufacturers, to employ even smaller sized, hermetically sealed, multi-pin connectors, such as ‘nano’-type multi feed-through pin electrical connectors, respective exterior and interior perspective views of a respective one of which are diagrammatically illustrated in FIGS. 2 and 3.
In particular, FIG. 2 is a pictorial or perspective front view of the exterior side of a multi feed-through pin, hermetically sealed nano-type connector, depicting pin-receiving sockets 21 of exterior distal ends of a plurality of feed-through pins 20, while FIG. 3 is a perspective interior view of the rear side of the nano-type connector of FIG. 2, depicting reduced diameter portions 23 of respective pins 20 to which wire bonds are to be made. Except for its smaller geometry parameters, a nano-type multi feed-through pin electrical connector has the same cross-sectional configuration as the micro-D type connector of FIG. 1; also, like a micro-D type connector, a nano-type multipin connector may contain from nine to one hundred (e.g., twenty-five) feed-through pins.
The geometry parameters of a nano-type multipin connector include a center-to-center spacing between adjacent pins 20 on the order of only 25 mils (namely, half that (fifty mils) of a micro-D sized connector) and a pin-installation bore diameter on the order of only twenty-two mils (approximately only half that (forty mils) of a micro-D sized connector). The diameter of the distal, socket portion of the feed-through pin of a nano-type connector is on the order of only eighteen mils, in order to conform with the geometry parameters of an associated nano-type plug through which external connections are provided. As a consequence, that portion of the pin which passes through the pin-installation bore must be even narrower, in order to accommodate a reduced wall thickness, annular dielectric sleeve through which hermetic sealing and support for the pin within the pin-installation bore is provided. To this end, the diameter of the reduced diameter portions 23 of the interior ends of the feed-through pins 20 of a nano-type connector is only twelve mils, which makes the pins too flimsy for effectively bonding at these locations.
Because of these very small geometry-based structural support and wire bonding problems, end users now are forced to use larger connectors, in order to have a pin diameter to which they can wire bond. Many manufacturers cannot build their products as small as they desire because a connector with a suitable interior pin diameter is too large for the proposed smaller unit design. A nano connector, which normally would hold twenty-five pins, but which has only nine pins, is much smaller than a normally populated nine pin micro-D connector. Also, manufacturers want to use standard connectors—often military standard connectors—and the available standards for multi-pin rectangular connectors are the sub-D connector standard with a 0.100″ pin spacing, the micro-D connector standard with a 0.050″ pin spacing, and the nano connector standard with a 0.025″ pin spacing.
When users/customers of these types of connectors reach the size limit of their device, because of the size limit of the micro-D connector, they become frustrated, because they know the nano connector exists, but they do not want to use it because of the smaller pin-to-wire required bond, its increased cost (due to the difficulty of building a part with 0.025″ pin centers), and its inferior hermetic reliability (due to marginal seal geometry).